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The recent synthesis and characterization of violet phosphorus (VP) demonstrate that it is the most stable allotrope of phosphorus, which could become a promising 2D layered semiconductor with potential applications in optoelectronic and electronic devices. However, experiments exploring the complex refractive index or permittivity have yet to be performed, hindering further application access. Due to the small size of the VP crystal sample available by the current growth method, the measurement for the complex refractive index is challenging. In this work, coherent acoustic phonon spectroscopy was performed first in the a–b plane using polarization-resolved pump-probe spectroscopy, revealing negligible anisotropy in the refractive index in the VIS–NIR regime (400–1000 nm). Then, the non-polarized reflectance spectra of VP films with different thicknesses on Si in the VIS–NIR regime were collected. The complex refractive index spectra were obtained by fitting the reflectance spectra with Fresnel's law considering multiple reflections in thin films. It was found that VP has high refractive indices and low extinction coefficients in the spectral range of 560–1000 nm, based on which a metasurface with VP nanodisks could achieve a high reflection band in the VIS–NIR regime by simulation. These results unveil the striking potential of VP for nanophotonics applications. [ABSTRACT FROM AUTHOR]

AlGaN LEDs emitting < 230 nm UV light were fabricated on sapphire substrates. We employed a quantum well (QW) with an extremely thin barrier to enhance the quantum confinement of holes, wherein the calculation showed that the topmost valence subband became X ± i Y -like and increased the transverse-electric polarized emission. Additionally, we modified the Al composition of the spacer layer situated between the QW and an electron-blocking layer, which significantly improved the current-injection efficiency. The combination and optimization of these structures produced an LED emission of 228-nm UV light with an output power of 1.4 mW at 150 mA. [ABSTRACT FROM AUTHOR]

The flexoelectric effect corresponds to the linear variation of the electric polarization of a material subjected to a strain gradient (i.e., during its mechanical bending). Unlike piezoelectricity, it also exists in non-centrosymmetric materials. Furthermore, due to the gradient term, its magnitude can increase as the size of the system decreases. Thanks to this effect, nanoscale systems could be used to harvest thermal vibration energy to power a microdevice. These could be multi-wall carbon nanotubes since they are known to bend easily in an elastic manner. However, it is very challenging to experimentally measure the flexoelectric behavior of a single multi-wall carbon nanotube due to its small size (less than 50 nm in diameter), to the low level of induced charges, and to the need to vary the imposed stress. To progress in this direction, a six-degree-of-freedom robot with a fiber tip is used inside a dual-beam microscope to pick up few single carbon nanotubes from a tangle and connect them to the fiber tip. After ion-soldering the two tips, each carbon nanotube is dynamically bent several times while monitoring the brightness of the bending area and its effective radius of curvature. This allowed us to demonstrate qualitatively the flexoelectric effect at the level of a single multi-wall carbon nanotube. [ABSTRACT FROM AUTHOR]